1. Field of the Invention
The invention relates to an electromechanically driven digital indicating device comprising an arrangement of seven flaps electromagnetically movable to two defined positions. The flaps are disposed in a housing at one plane thereof so as to form an "8"-shaped figure. The device includes driving electromagnets to move the flaps so that, by actuation of certain combinations of flaps, digits are to be represented.
2. Background of the Prior Art
Generally speaking, digital indicating devices which are electromagnetically driven have a design wherein all figures from "0" to "9" may be represented in a matrix of seven bars or segments in the form of a stylized "8". In a simple known embodiment of this kind of digital indicating means (German Offenlegungsschrift No. 22 00 469), there is an indicating panel arranged at the front side in which there is a system of gaps provided for the digits to be indicated. Behind each gap, an electromagnetically actuatable segment is arranged which may be moved to an indicating or non-indicating position. To accentuate the indicating part of the segment, this part of the segment is provided with a coloring which contrasts against the surface of the panel.
In the non-indicating position of the segment, it closes the gap and is of the same color as the surface of the panel so that at a certain distance, the closed gaps of the system are visually hardly perceivable. By simultaneously moving a combination of at least two up to maximally all seven segments to the indicating position, all the digital symbols from "0" to "9" may be represented. The electromagnetic devices for moving the segments consist of magnetic coils with an iron core so that a magnetic field is built up when the coil is energized. Depending on the direction of the magnetic field, a permanent magnet connected to the segment is attracted or rejected. This means that the rotatably mounted segment is moved between an indicating and a non-indicating position.
Another embodiment of the above described electromagnetic indicating devices has become known through Offenlegungsschrift No. 24 48 633. This indicating device consists of a front window plate which, for making visible the indicating elements, has seven longitudinal openings, the openings being arranged a certain distance from each other but in the shape of an "8". In a plane behind the front window plate, there is a bearing plate mounted at a certain distance on cylindrical elements. The plate serves to pivotally mount the seven indicating elements. The indicating elements are arranged so that they may be moved from one stable position, where they are invisible behind the front window plate, to another angular stable position where the indicating elements, which are in a contrasting color with respect to their surroundings, appear in the opening behind the front window plate. Accordingly, when the elements are read in connection, they represent a symbol of a figure. For mounting the indicating elements, the mounting plate is provided with a plurality of flanges which extend forwardly to the front window plate. In another plane behind the bearing plate, that is, in a third plane, there is a back plate which is borne by two distance pieces by the bearing plate. The back plate serves to position and to fasten the seven magnetic cores which extend forwardly to the bearing plate. The front window plate, the bearing plate and the back plate are screw-connected via rod-shaped distance pieces and bushings in a firm position to each other.
The known electromechanical indicating devices are disadvantageous especially because, for making one decade of figures, a relatively large number of parts is required. The position of the parts with respect to each other depends on a lot of tolerances, particularly since the cooperating parts are arranged in three planes. This means that a high degree of attention and care is required to produce the parts as well as to mount them to a complete indicating device for one digit. If it is required to protect the movable parts and especially the very sensitive bearing parts against dirt, there is no other choice but to include the whole construction within an external housing.
With the known solution, it is also disadvantageous that the position of the pivotal magnets with respect to the magnetic field of the coil cores is not optimal. Since the pairs of mounting flanges extend forwardly to the front window plane, there unavoidably are, between the permanent magnets of the flaps and the electromagnets pertaining thereto, wide air gaps. The efficiency of the magnetic circle is therefore very small because of the big air gap which the magnetic force has to overcome. This means that, for moving the segments, current pulses of considerable strength are required which cannot be taken directly from an electronic driving circuit without using additional amplifying circuits. This, however, means rather increased production costs. Due to the lower efficiency of the magnetic path and since the indicating means are not protected against dirt, it is not possible to achieve short switching times. This, of course, unfavorably influences the expenses which have to be made with respect to the electronic parts for producing the control pulses (one decoder required only).
With regard to the aesthetic impression of the number representation with respect to its readability, the known digital indicating device is not an optimal solution since the number is produced by pivoting the colored segments or bars into the window attributed thereto. It is unavoidable that, at the transition between two segments, there will be gaps which are perceived as an unwelcome interruption in the figure line.
In another known digital indicating device as described by German Offenlegungsschrift No. 28 04 153, an attempt is made not to represent the figures by individually pivotal segments but in the form of an uninterrupted line. Here, it shall be possible to use also an internal light source. In this solution, the electromechanically actuatable segments are moved off to realize partially or wholly the "8"-shaped figure arranged thereunder. Of course, in this arrangement, the seven slots in the cover plate of the housing form a single uninterrupted eight-shaped window which allows the release also of an "8"-shaped figure under the cover plate. The pivotal covering segments arranged to release the figure especially at the two sides of the figure running from top to bottom are, however, symmetrically arranged and, in the range of the median bar, interrupt the line of the figure "8". For each figure to be indicated, in which of the two lateral segments only one is to be moved to the uncovering position, in the range of transition of the median bar into the lateral bars, essential parts of the figure remain covered. The figure forming line is thereby partially interrupted. This essentially worsens the readability of the corresponding figure representations, that means of the 2, 4, 5, 6 and 9, and gives the impression of an incomplete representation of the figure.